1. Field of the Invention
The subject invention generally relates to transducers and apparatus and methods for making same and, more specifically, to diaphragm elements, edge mounted diaphragms, methods and apparatus for making same, and to the fabrication of very thin metal diaphragms for low-pressure transducers, as well as to such fabricated metal diaphragms and to apparatus and fixtures for fabricating same.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior-art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent.
Difficulties have been encountered in the use of conventional methods of manufacturing thin metal diaphragms for transducers, particularly when the diaphragm itself and the transducing element are intimately joined together such as in a device incorporating a strain gauge bonded to the diaphragm. In such devices, the so-called "machined diaphragm" has had certain advantages provided proper material is used and adequate stress relieving is employed. However, such conventional machined diaphragms have been costly to produce and require excessive or exorbitant quality control monitoring to avoid improper machining of the diaphragm surface.
The use of welding techniques has been limited primarily to seam welding which is satisfactory when the diaphragm serves as a force collector only, with a mechanical link to the transducing element.
Transducer diaphragm electron beam welding has been described in the book ELECTRON-BEAM WELDING: PRINCIPLES AND PRACTICE, by A. H. Meleka (McGraw-Hill, 1971). In particular, that book on pages 272 and 273 shows a pressure transducer having a thin diaphragm electron beam welded to the end of a transducer tube. The diaphragm in that pressure transducer had a diameter smaller than the adjacent end of the tube to enable an axially impinging electron beam to provide a circumferential weld in the diaphragm and a corresponding circular portion of the transducer tube.
To this end, the diaphragm first had to be secured to the transducer tube by means of light weld tacks, produced with a miniature resistance welder. The electron beam weld was carried out by rotating the transducer below the electron beam.
One disadvantage in terms of time, labor, quality, equipment and cost expenditure of that prior proposal stems from the need of having to employ resistance welding, that is a welding technique other than electron beam welding, for initially assembling the diaphragm with the transducer tube. Another inherent disadvantage stems from the fact that the circumferential welding technique disclosed in the cited book in practice leaves an unwelded circular region between the diaphragm and the inner circumferential portion of the transducer tube, as may be seen from FIG. 7.46(b) of the cited book. This renders the diaphragm characteristics non-linear at the cross-over region from negative to positive pressures, inasmuch as the effective diaphragm diameter varies somewhat abruptly as the diaphragm is alternately urged away from and pressed onto the transducer tube.
Also, the technique under consideration produces a rather coarse weld, as may be seen from FIG. 7.46(c) of the cited book.
With conventional electron beam welding techniques, attempts at deep welding penetration frequently foundered on resulting evaporation. As shown, for instance, in FIG. 3.4 of the cited book, mere melting of a metal by the electron beam does not produce deep penetration (see pp. 82 to 85).
On the other hand, deep penetration tends to be accompanied by evaporation of the material impacted by the electron beam, as illustrated by FIGS. 3.4(c) and 3.5, pp. 85 to 89, of the cited book.
Reference may in this respect also be had to Japanese Patent Publication 47-31815 by Matsushita Denki Sangyo Kabushiki-Gaisha (inventor Uno Yoshihiro), published Aug. 16, 1972.
In particular, as that Japanese patent publication shows with the aid of FIG. 1(a) to (d), conventional electron beam welding tends to proceed through different states, culminating in the formation of a hole or indentation of constant shape, which remains open because of an equilibrium condition as explained in the cited Japanese patent publication and the above mentioned book.
The Japanese patent publication thus rejects attempts to weld thin films to thicker metal sheets by an axially impinging electron beam. Rather, the Japanese patent publication proposes that grooves of V-shaped cross-section be cut into the thicker metal sheet adjacent the applied thin film, in order to diminish thermal capacity and conductivity of the metal sheet or, in other words, diminish the difference between thermal capacity and conductivity between the metal sheet and thin film at the welding sites, providing edged zones in the metal sheet at the thin film of a thickness more comparable to that of the thin film.
In the case of most transducers, it would, however, not be practical or feasible to cut deep grooves into the transducer tube or body in the vicinity of the diaphragm. Also, though the Japanese patent publication shows the cutting of rather deep grooves for edge zone equilization purposes, it appears that the actual electron beam weld is, nevertheless, rather shallow at the periphery of the thin film and thicker metal sheet, without much radial penetration.
The proposal according to the Japanese patent publication also requires the use of force-applying loads for holding the thin metal film in completely tight contact with the underlying metal sheet. In particular, this Japanese reference requires these force-applying loads to leave free edge portions at the film margins of about 0.1 to 2 mm for the electron beam welding process.
In brief, the proposal according to the Japanese patent publication would not be suitable for most transducer applications, which would at any rate require a closed annular weld and, therefore, also an annular V-shaped groove, if implementation of that proposal were to be attempted.
Reference may in this respect also be had to U.S. Pat. No. 3,458,683, by D. A. Canonico et al, issued July 29, 1969. In the context of electron beam welding of a thin metal foil in a sandwich-type arrangement, Canonico et al expressly deprecate the use of electron beam welding methods which involve overlapping or butting of the parts followed by directing a suitable electron beam through the metals or along the formed joint to form the weldment, as otherwise satisfactory in the welding of many metallic materials.
In contrast to the utilization of such techniques, which Canonico et al advise against, they propose to employ an axially extending electron beam which is passed through an annular retaining member and two junctures between the retaining member and a retained foil and between that retained foil and a work piece.
Canonico et al thus obtain a welding fillet which extends through the retaining member and retained foil into the underlying work piece, while also extending somewhat irregularly about an aperture in the annular retaining member.
The axial electron beam welding technique proposed by Canonico et al inevitably leaves unwelded annular regions between the work piece and the foil and between the foil and the retaining member. If attempts were made to apply the proposal of Canonico et al to the manufacture of transducers, essentially the same drawbacks in terms of non-linearity of cross-over characteristics would be encountered, as mentioned above, with respect to the pressure transducer welding technique shown on pages 272 to 273 of the cited ELECTRON-BEAM WELDING book. As can also be seen from page 182 of that book, even the relatively lower shrinkage distortion of electron beam welding would tend to bow or otherwise distort the retained thin film or diaphragm intersected perpendicularly by the welding fillet.
As may further be noted from pages 282 et seq. of the cited book, conventional electron beam welding techniques require the provision and utilization of rather complex and expensive jigs and fixtures which equal and even surpass complex fixtures of the type disclosed in U.S. Pat. No. 4,034,182, by Schlosser et al, issued July 5, 1977.
That existing jigs and fixtures for electron beam welding offer no practical solution for the manufacture of edge mounted transducer elements may further be seen from U.S. Pat. No. 3,780,412, by B. J. Millard, issued Dec. 25, 1973. In particular, Millard proposes the use of rods passing through assembled cylindrical parts and undisclosed "suitable clamping means" for holding the assembled parts together.
The lack of helpful teaching in the state of the art may also be seen from U.S. Pat. Nos. 1,548,106, 1,589,962, 3,624,342, 3,856,995, 3,991,321 and 4,029,911, which propose various clamping, ultrasonic and screw fastener techniques unsuitable for miniature transducers and similar equipment.
For completeness' sake, reference is also made to U.S. Pat. No. 3,816,698, by Wellendorf et al, issued June 11, 1974, and disclosing an arrangement for producing screened printing forms with the aid of an electron beam. While that patent has been cited as of interest in the parent application, it does not evince any particular pertinency.